xgrammar Vulnerable to Denial of Service (DoS) by abusing unbounded cache in memory
Summary
Xgrammar includes a cache for compiled grammars to increase performance with repeated use of the same grammar. This cache is held in memory. Since the cache is unbounded, a system making use of xgrammar can be abused to fill up a host's memory and case a denial of service. For example, sending many small requests to an LLM inference server with unique JSON schemas would eventually cause this denial of service to occur.
Details
The fix is to add a limit to the cache size. This was done in https://github.com/mlc-ai/xgrammar/pull/243
An example of making use of the new cache size limit can be found in vLLM here: https://github.com/vllm-project/vllm/pull/16283
Impact
Any system making use of Xgrammar and taking requests as input from potentially untrusted parties would be vulnerable to this denial of service issue.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | xgrammar | < 0.1.18 | 0.1.18 |
References
- https://github.com/mlc-ai/xgrammar/security/advisories/GHSA-389x-67px-mjg3
- https://github.com/mlc-ai/xgrammar/pull/243
- https://github.com/vllm-project/vllm/pull/16283
- https://nvd.nist.gov/vuln/detail/CVE-2025-32381
- https://github.com/mlc-ai/xgrammar
- https://github.com/pypa/advisory-database/tree/main/vulns/xgrammar/PYSEC-2025-235.yaml
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-770- Platform
- Python (PyPI)
- Package
xgrammar- Disclosed
- 09.04.2025
- Updated
- 11.10.2026 15:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2025-235 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-389x-67px-mjg3 - CC BY 4.0
Vulnerability history: xgrammar
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 4
- First → latest
- 04.2025 03.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 2
- Medium 2
Disclosures per year
- 2025: 3
- 2026: 1
-
xgrammar Vulnerable to Denial of Service (DoS) by abusing unbounded cache in memory this entry
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